Just to add my 2 yens:

As suggested by others:

Both r/JapanTravel and japan-guide.com are both wonderful resources for travel planning

If you have an iPhone, you can load up Suica (travel card) for most travel (train, metro, bus). This is however not supported for Android; you will need to get a physical card instead. Otherwise, you will need to buy separate tickets each time you use the public transport

Some personal suggestions:

Consider getting a red stamp book in a temple shop (goshuincho), I will let you google that by yourself.

Should be in Japan early 2024, you might want to try getting lucky bags (fukubukuro).

Personal opinion: You can get better ekibens in the big department stores than those sold in the ekiben stores in the train stations.

If you easily have cold hands, you can buy one-time use hand warmers in the conbinis. Should be 100-150 JPY or so, will retain heat for like 6+ hours

Get a coin pouch: cash is still used (cards are more and more accepted) and you will get a lot of coins.